A width of a metal wiring made up of Al, Cu, and so on becomes narrow in accordance with high integration of a semiconductor element. Accordingly, improvement in electromigration (EM) resistance is required. It is desirable to grow a densest surface of a metal crystal in a columnar state when a metal film for wiring is deposited by sputtering to improve the EM resistance. It is also desirable to deposit a barrier film made up of TiN and TaN formed as a base of the metal wiring by the sputtering such that a densest surface thereof similarly grow in the columnar state to enable the above.
A TiN (titanium nitride) film is suitable as the barrier film for an Al wiring. The TiN film is obtained by sputtering a sputtering target made up of, for example, high-purity Ti in a nitrogen atmosphere. It is required to miniaturize a crystal grain size of the metal constituting the sputtering target, and to randomize a crystal orientation to perform the sputtering deposition such that the densest surface of the barrier film becomes the columnar state. Further, for example, it is required to eliminate residues of a cast structure (ghost grain) to improve uniformity of a sputtering film.
In a conventional titanium target, improvement of characteristics is enabled by controlling an impurity amount and a heat conductivity, or controlling a crystal direction. For example, a titanium target of which purity and heat conductivity are increased to enhance the uniformity of the sputtering film is known. Besides, a titanium target of which crystals are oriented in a certain direction to increase a deposition rate is known. On the other hand, the titanium target tends to become large such that a diameter thereof exceeds 300 mm, a thickness thereof becomes 8 mm or more, and so on. This arises from a large sizing of a silicon wafer. It is also required in the large sized titanium target as stated above to increase controllability of the crystal grain size and an orientation state of the crystals. Besides, it is required to increase stability of a sputtering rate.